Problems with ajax in a for loop

Question

I am having a problem with ajax in a for loop.

I have this code:

function start()
{
    for(var i=1;i<=27;i++)
    {

        var letter = getLetter(i);      
        doAjax(letter);
    }

}

function doAjax(letter)
{
    $.post( "ajax_add.php", { let: letter})
        .done(function( data ) {
            document.write(letter + "<br />");
        }); 
}

and it outputs: a b c e d %23 h f i k j g l m q n o p r s u t v w x z y

or a different kind of order in stead of: %23 a b c d e f g h i j k l m n o p q r s t u v w x y z.

If I remove the ajax it works just fine:

function start()
{
    for(var i=1;i<=27;i++)
    {

        var letter = getLetter(i);      
        doAjax(letter);
    }

}

function doAjax(letter)
{
        document.write(letter + "<br />"); 
}

getletter function:

function getLetter(i)
{
        var pag = "";
        switch (i)
        {
            case 1:
                pag = "%23";
                break;
            case 2:
                pag = "a";
                break;
            case 3:
                pag = "b";
                break;
            case 4:
                pag = "c";
                break;
            case 5:
                pag = "d";
                break;
            case 6:
                pag = "e";
                break;
            case 7:
                pag = "f";
                break;
            case 8:
                pag = "g";
                break;
            case 9:
                pag = "h";
                break;
            case 10:
                pag = "i";
                break;
            case 11:
                pag = "j";
                break;
            case 12:
                pag = "k";
                break;
            case 13:
                pag = "l";
                break;
            case 14:
                pag = "m";
                break;
            case 15:
                pag = "n";
                break;
            case 16:
                pag = "o";
                break;
            case 17:
                pag = "p";
                break;
            case 18:
                pag = "q";
                break;
            case 19:
                pag = "r";
                break;
            case 20:
                pag = "s";
                break;
            case 21:
                pag = "t";
                break;
            case 22:
                pag = "u";
                break;
            case 23:
                pag = "v";
                break;
            case 24:
                pag = "w";
                break;
            case 25:
                pag = "x";
                break;
            case 26:
                pag = "y";
                break;
            case 27:
                pag = "z";
                break;
        }

        return pag;
    }

and the ajax_add.php just prints out 1 letter i dont even use the incoming data in the code above.

Thanks!